In his Theory of the avant-garde, Peter Bürger defines the historical avant-garde as Dada, Surrealism, and Constructivism, while classifying such movements as Cubism as modernist. According to Bürger, what distinguishes an avant-garde movement from a modernist one is that the avant-garde rejects aestheticism, an exclusive concern with formal qualities, in favour of integrating art with life.

Bürger contends that the historical avant-garde failed to achieve this goal. He argues that the neo-avant-gardes of the 1950s and 1960s were a farcical repetition of this failure. For Bürger, the historical avant-garde’s failure was heroic, but the neo-avant-garde’s repetition of that failure actively works against the goals of the historical avant-garde.

However, this alleged common aim of the avant-garde to integrate art and life is obvious bullshit. Yes, there were avant-garde artists who did have that aim, but there was also others who didn't. Having that aim is neither a necessary nor a sufficient property of being an avant-garde art work, artist, or movement.

In his Theory of the avant-garde, Renato Poggioli takes another tack. He identified four essential features belonging to the avant-garde:

alienation from bourgeois capitalist society

activism and antagonism towards the public and public institutions, especially official and academic art

a fundamental break with the past

self-consciousness as an elite vanguard of the future.

Basically, according to this theory, all you need is a bourgeois capitalist society with official and academic art institutions, and certain attitudes towards those institutions and that society. What matters is not whether a particular art work was made in 1910, 1960, or 2010 but its relationship with the official art institutions of the society it inhabits.

Hence, rather than historical and neo-avant-gardes, we have the intertemporal avant-garde.